| Rice plays an important role in food security in China. Using the heterosis of inter-subspecies hybrids is one of the important approaches to increase the rice yield. However, the F1 semi-sterility has been a major barrier for the utilization of the strong heterosis between indica and japonica. The discovery of wide compatibility genes (WCGs) has brought breeders hope for breaking the fertility barrier. The wide compatibility gene S5-n has been incorporated into breeding lines to utilize the strong heterosis of indica-japonica hybrids in hybrid breeding. However, with the broadening of parents used in rice breeding, some hybrids still showed semi-sterility despite the present of S5-n allele in one of their parents. In order to take the full advantage of the strong heterosis of inter-subspecific hybrids, it is necessary to accumulate the wide compatibility genes found in useful genetic backgrounds to overcome various sterilities in inter-subspecific hybrids. The genetic study of hybrid sterility led to the finding of a neutral allele or wide compatibility allele.Aus is the summer cultivation in India subcontinent Bengal area, they are mostly insensitive for photoperiod, and have extensive diversities on heredity characteristics. In this research, one of parents Ingra has red pericarp, belonging to Aus, Cpslo17 and Ketan Nangka are Java carrying S5-n, IR36 is a representative test in Indica, but it is compatible in S7 locus.In this study, the hybrid semi-sterility locus was found by constructing chromosome 7 molecular linkage maps, and the result showed it was S7 locus. Fine mapping of S7 and cytological studies were done and the main findings are as followings:1. Mapping of rice indica-japonica hybrid sterility gene S7 and cytological observationsIn this study chromosome 7 molecular linkage maps of the three-way population Ingra/IR36//Cpslol7 and Ketan Nangka/Ingra//Cpslol7, F2 population Ingra/Cpslo17 were constructed seperatedly, and there was only one QTL was reponsible for spikelet semi-sterility, which was located between RM5543 and RM1135(the span is 2.5M) on chromosome 7. The location was the same to the results reported by Yanagihara et al. (1992), so it was speculated S7 locus. In the following, the real cause of sterility was investigated in Ingra/IR36//Cpslo17 population. The results showed that, I2-KI staining pollen fertility was normal, but parts of embryo sac were abnormal when scanned by confocal microscope. Regression analysis showed that spikelet fertility and embryo sac fertility were significantly positively correlated, and R2=0.8526. Correlation analysis also showed that embryo sac fertility and spikelet fertility was significantly correlated, and the correlation coefficient was 0.9234. So embryo sac abortion was the main reason for semi-sterility.2. The fine mapping of hybrid sterility gene S7Plants of BC1F1 which carrying locus S7-n/S7-cp and S7-kn/S7-cp outside of both close markers and carrying S-ailS-cp between close markers, and seed setting rate was less than 55% were choosed and then these plants were self-crossed to generate BC1F2. The BC1F2 were used for fine mapping of S7. In the end the S7 was located between RM5543 and TI44, and the span was 170kb. Gene prediction analysis indicated that in this region there were 19 open reading frames, of which there were six for encoding function proteins, and 10 for encoding hypothetical proteins, and three for encoding unknown proteins. The study has laid a good foundation for further fine mapping, cloning and the molecular mechanism of S7 study. |
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